Refiner segment

ABSTRACT

A refiner segment (1) for disc refiners is formed with a pattern of bars (2,4) and grooves (3,5), and flow restrictions (6) are located in the grooves (5). Through apertures (8) in the bars (4), the grooves (5) communicate with each other so that the grooves have free communication outward and inward via the apertures (8).

This invention relates to refiner segments in a disc refiner forrefining fiber material, which can be wood chips or pulp, which isentirely or partially defibered.

The disc refiner comprises two opposed refiner discs, one or both ofwhich can be rotatable. On the refiner discs refiner segments arelocated, which are formed with a pattern of bars and intermediategrooves. The refiner discs are positioned so that the refiner segmentsform a disc gap, through which the fiber material is intended to pass,whereby the refining is carried out by the bars of the refiner segments.

The bars and grooves of the refiner segments normally extendsubstantially radially. The pattern can be divided into different zoneslocated outside each other.

During the refining of fiber material with high concentration, andespecially at high energy charges, it was found necessary to insert flowrestrictions, so-called cross-bars, in the grooves in the refinersegments in order to prevent unprocessed material from passing outthrough the disc gap. These cross bars, however, constitute a hindrancefor the steam, which during the refining develops in the disc gap.Consequently a high steam pressure arises in the disc gap. This highsteam pressure has a negative effect on the capacity and operatingstability of the refiner, and it also limits the possible energy charge.The steam developed, thus, is forced upward out of the grooves by theflow restrictions and disturbs the material flow through the disc gap.

One way of solving the aforesaid problem is to supply dilution water tothe disc gap in order to condense the steam. This way, however, causes areduction in the material concentration to such a low level that thepulp quality deteriorates.

The present invention provides a solution to the problem of high steampressure in the disc gap, without giving rise to other inconveniencesduring refining. According to the invention, the bars on the refinersegment are formed with apertures which interconnect adjacent grooves,so that the grooves communicate freely outward and inward via theapertures. This implies that the steam developed is not obstructed bythe cross bars, but can flow through the apertures to the adjacentgroove and further outward or inward. The steam pressure resulting inthe disc gap increases in the outward direction to a maximum andthereafter decreases toward the outlet of the disc gap. This impliesthat steam formed in the interior part of the disc gap, i.e. inside ofsaid pressure maximum, flows inward, while steam forming in the outerpart of the disc gap flows outward to the outlet of the disc gap.

The invention is described in greater detail in the following, withreference to the accompanying drawing showing two embodiments of arefiner segment according to the invention, in which drawing

FIG. 1 shows a refiner segment seen perpendicularly to the surface,

FIG. 2 is a section along II--II in FIG. 1, and

FIG. 3 shows another embodiment of a refiner segment.

Refiner segments 1 according to the Figures are formed with a pattern ofsubstantially radial bars and intermediate grooves. The pattern isdivided into two zones, an inner one and an outer one. The bars 2 andgrooves 3 in the inner zone are coarser than the bars 4 and grooves 5 inthe outer zone. In the outer zone flow restrictions 6 are located. Inthe embodiment according to FIGS. 1 and 2 flow restrictions 7 are alsoprovides in the inner zone, but such restrictions are not provided inthe embodiment shown in FIG. 3. The flow restrictions 7 in the innerzone do not extend all the way to the upper surface of the bars 2, whilethe flow restrictions 6 in the outer zone extend up to the level of theupper surface of the bars 4. In the outer zone the grooves 5 communicatewith each other through apertures 8 in intermediate bars 4. Each ofthese apertures 8 is located in close connection to a flow restriction 6and in a radial direction outside the same. The apertures 8 preferablyare U-shaped and extend a distance downward from the upper surface ofthe bars 4.

The apertures 8 are located so that there is free communication bothoutward and inward via the apertures 8 and grooves 5. The steamdevelopment during the refining is especially high in the outer zonewhere the steam pressure maximum is located. The apertures 8, therefore,provide a possible passage for the steam over to adjacent grooves 5, inwhich the steam can continue to flow outward or inward and possibly viaadditional apertures 8 and grooves 5 finally leave the disc gap at theoutlet or inlet thereof.

In the embodiment according to FIG. 3 the apertures 8 and flowrestrictions 6 are located so that each aperture is located, counted ina radial direction, immediately outside a flow restriction in a grooveand immediately inside a flow restriction in adjacent grooves. Thereturn flow of the steam through grooves is thereby minimized, becauseit is obstructed by the flow restrictions.

In cases when the refiner segment is formed with more zones, theapertures in the first hand should be placed in the outermost zone wherethey will be most useful due to the great steam formation in said zone.

The invention, of course, is not restricted to the embodiments shown,but can be varied within the scope of the invention idea.

I claim:
 1. An improved disc refiner for refining fibrous materials,said disc refiner having a refiner segment formed with a patternincluding a plurality of radially disposed bars having an upper surface,a plurality of grooves radially disposed intermediate said bars, and aplurality of flow restrictions traversing said grooves between adjacentones of said bars and extending upward in said grooves to said uppersurfaces of said adjacent ones of said bars, at least one of said barsincluding connecting means for enabling direct communication between apair of said grooves adjacent said at least one of said bars.
 2. A discrefiner as claimed in claim 1 wherein said pattern includes a pluralityof zones extending radially from an innermost zone to an outermost zone,and said connecting means on said at least one of said bars is disposedin said outermost zone.
 3. A disc refiner as claimed in claim 1 whereinsaid plurality of said bars includes said connecting means, and whereineach of said connecting means is associated with one of said flowrestrictions and is disposed in a location radially outward from saidone of said flow restrictions with which it is associated.
 4. A discrefiner as claimed in claim 3 wherein said pattern includes a pluralityof zones extending radially from an innermost zone to an outermost zone,and said connecting means on said at least one of said bars is disposedin said outermost zone.
 5. A disc refiner as claimed in claim 1 whereinsaid plurality of said bars includes said connecting means, and whereineach said connecting means is disposed in a location radially outwardfrom one of said flow restrictions in a first groove, and radiallyinward from another of said flow restrictions in a second grooveadjacent to said first groove.
 6. A disc refiner as claimed in claim 5wherein said pattern includes a plurality of zones extending radiallyfrom an innermost zone to an outermost zone, and said connecting meanson said at least one of said bars is disposed in said outermost zone. 7.A disc refiner as claimed in any one of claims 1-6 wherein saidconnecting means comprise U-shaped channels extending downwardly fromsaid upper surface of said bars.